Governors' Wind Energy Coalition

Former vice president Joe Biden speaks during a campaign rally in Philadelphia in May. (AP Photo/Matt Rourke)

Several White House hopefuls unveiled ads this week trashing President Trump for refusing to crack down on polluters and work with other world leaders to slow global warming.

The advertising blitz comes as negotiators from other countries meet at a United Nations climate summit in Madrid try to hammer out the details of implementing the Paris climate accord, an agreement from which Trump has promised to withdraw.

The latest candidate out with a climate ad is former vice president Joe Biden, who is leading most national polls.

“The rest of the world hasn’t given up on the Paris climate accord,” Biden said in the nearly two-minute spot released this morning. “They’re pushing it. They know it’s essential to human existence.”

The new spots are the latest sign that climate change, once an afterthought in past presidential elections, has become a key issue in the race for the Democratic nomination. Recent polling by The Washington Post and the Kaiser Family Foundation shows that Americans increasingly see climate change as a crisis, with Democrats more likely than Republicans to say that human activity is fueling rising temperatures.

The Biden campaign, in the ad titled “The Only Way,” is doubling doubled down on its argument that the former vice president has the best chance of beating Trump in the general election.

“The first and most important plank in my climate proposal is: Beat Trump.” Biden said.

His campaign is rolling out the ad online on the fourth anniversary of the approval of the international climate accord in Paris. Biden’s team is spending a five-figure sum to promote the video in Iowa, the first state in the nation to vote in the 2020 nomination.

Biden, noting that no amount of U.S. greenhouse gas reductions will matter if other countries continue polluting, has made rejoining the Paris agreement of the fulcrum of his climate policy.

The U.N. talks also gave other candidates an opening to put a spotlight on global warming: Former New York mayor Mike Bloomberg was in Madrid, in a prime spot to take shots at Trump for abandoning the climate agreement.

“The reason I am here in Madrid is really pretty simple: I am here because no one from the White House is here,” Bloomberg told an overflow crowd on Tuesday before flying to San Francisco to address the American Geophysical Union’s annual conference as part of a whirlwind climate tour.

His campaign also released an ad focused on a different impact of climate change — wildfires in California.

His spot, called “A Champion For Climate,” features dramatic images of burning hillsides in California and calls Trump a “climate denier” who “consistently sides with polluters.” The billionaire’s campaign is promoting the online-only spot in California.

And businessman Andrew Yang, who has built his candidacy on a signature policy of paying every American adult $1,000 a month, is trying to broaden his appeal by turning to the issue of climate change in his latest ad in Iowa.

“Iowa has suffered devastating floods and tornadoes,” Yang said in the spot, which his campaign is spending about $500,000 to broadcast in Iowa. “Other states, scorching wildfires and super hurricanes. Our climate is in crisis.”

Much of the Midwest, including stretches of western Iowa along the Missouri River and eastern Iowa along the Mississippi, was inundated earlier this year with record flooding thought by scientists to have been made worse by the warmer and more humid atmosphere.